The present invention relates to a defect detection method and the device for detecting a defect such as a foreign matter defect in the form of a contaminant, a discoloration defect, a deformation or pattern defect, etc. for LSI wafer patterns, etc.
Among conventional visual inspection systems, for example, the one described in Technical Journal, Vol. 87, No. 132 (1987), pp. 31 to 38, The Institute of Electronics and Communication Engineers of Japan is well known. Such a system is shown in FIG. 23 where a circuit pattern on a wafer 1 lighted with a lamp 2 is enlarged and detected with an image sensor 4 through an object lens 3, whereby a variable density image such as a gray scale image of the circuit pattern is obtained. The detected variable density image is compared with the image of the preceding chip 7a (adjacent chip) stored in an image memory 5 in a defect judgment circuit 6 for performing defect judgment. The detected image is simultaneously stored in the image memory 5 to be used for comparison with the next chip 7b.
An example of defect judgment is shown in FIG. 24. A detected image and a stored image are aligned in an alignment circuit 6a and a difference in images between the aligned detected image and stored image is detected with a difference or subtraction image detection circuit 6b. A defect is detected by binarizing the detected difference image in a binarization circuit 6c. With the above arrangement, a defect 8d existing in the detected image can be detected. As an example of devices of this type is described in SPIE Vol. 772, Optical Microlithography 6 (1987), pp. 247 to 255.
In the prior art systems, a defect is detected by finding an unmatched point between corresponding patterns, so that the detected defect has to be observed with other observation apparatus, for example, an optical microscope or a SEM to identify the kind of the defect such as deformation defect, a discoloration defect or a foreign matter defect.